# [GRASS-user] Cost Path

ALT SHN i.geografica at alt-shn.org
Fri Feb 10 15:30:49 EST 2012

```@ Roberto

Thank you for the hint. It's a nice way arround for a future purpose.

The friction map I am using was build from various inputs, one of them the
DEM (slope). So, if I understood right, using r.walk would be redundant
beacause slope and altitude are already considered in the friction map.

Best Regards,

André

2012/2/8 Roberto Marzocchi <roberto.marzocchi at gmail.com>

> I have resolved with:
>
> r.walk -k elevation=your_dtm friction=your_friction output=*walkout*start_points=A stop_points=B
>
> afterwards
>
> r.drain -c input=*walkout* output=drainout vector_points=B
>
> perhaps it is need a filling of the dtm and also of walkout map in order
> to avoid aq loop effect
>
> All the best,
> Roberto
>
>
> 2012/2/7 Moritz Lennert <mlennert at club.worldonline.be>
>
>> On 07/02/12 14:39, ALT SHN wrote:
>>
>>> Hello list,
>>>
>>> I have a raster obtained through r.mapcalc whose cells values represent
>>> friction or cost.
>>>
>>
>> I suppose that is friction per cell.
>>
>>
>>  To finish my study I'm lacking one final step - calculate the least cost
>>> path!
>>>
>>> How do I do it? I've tried r.cost but the result is not wat I expected -
>>> My desired output is just a line from A to B, crossing the least valued
>>> cells.
>>>
>>
>> Use r.cost with the coordinate of (or the vector or raster file
>> containing) A as start point. Then r.drain with B as starting point.
>>
>> Moritz
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>
>

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